Signaling system



latcntcd Aer. 7 g 7 UNITED STATES PATENT", cr mes,

LELAND J. simcY, or nLooMrInLn, new JERSEY, assielvon 'ro wEsrnR-n ELECTRIC COMPANY. INCORPORATED, or NEW Yon-K, n. Y., A CORPORATION or new YonK.

SIGNALING SYSTEM.

Application filed September 15, 1921. Serial No. 500,767.

To 675 whom, it may canoe m. 7

Be it known that I, LELAND J.'STACY, a citizen Olf the United States, residing at Bloomfield, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Signaling Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to signaling systems and more particularly to methods and means for transmitting an audible ringing signal to a calling subscribers station to indicate that the called subscribers station is being signaled. i

In some circuits of this nature being used there is considerable variation in the 'character of the signal transmitted to the station of the calling subscriber due to variations in the ringing current for signaling the called subscriber, which current is also used tosig nal the calling subscriber that the called sub scriber is being signaled.

In some systems which are now widely used, the audible ringing signal is obtained from the regular ringing current source which is generally of a frequency of approximately 16 cycles per second. The signaling tone is due to the higher harmonic components of audible frequencygenerally the so-called slot ripples of the ringing machine. These harmonic components being superimposed upon the 16 cycle current wave are accordingly subject to modulation twice each cycle or 32 times per second. This re sults in a characteristic tone which hascome to be well lmown and which differs from that obtained when the tone is supplied without interruption from a separate source. In the patent to Philip Husta, No. 1,512,- 933, granted October 28, 1924, a circuit arrangement employing a separate source of current :lor the signaling tone is disclosed which is llil'G/Q- from the disadwnitages outlined above.

l t an object ()if this invention. to provide an improved arrangement for modulating signaling current from a separate source, similar to that disclosed in the aforesaid copending application of Philip Husta, but arranged to simulate the tone now obtainediin the well known circuits new extensively employed.

It is further object of this invention to provide means whereby the electrical constants of the circuit for supplying ringing tone current are maintained approximately the same regardless of whether or not the tone is being applied to a subscribe-rs line.-

This is a desirable feature since the tone circuit may in addition to its use for an audible ringing signal be also used for a variety of other signals inconnection with the operation of the telephone otlice and it would be objectionable if the character of the tone changed each time that the tone current is applied to the calling subscribers line.

lit is also an object to provide means whereby the periodic modulation of the signaling current is prevented from causing audible disturbances in other signalingcircuits also supplied from the common source of tone current. I

For a more complete understanding of the invention reference may be had to thefollowing description in connection with the accompanying drawing F 1 of which illustrates one embodiment of the invention.

Figs. 2, 3 and 4; of the drawing show, respectively, the wave forms of the outputot the ringing generator, of the signaling currenttransmitted to th calling subscriber in one of the above mentioned systems and of the signaling current transmitted to the calling subscriber in the embodiment of the inveir tion shown in Fig. 1. J

In the drawing, a calling and a called subscribers station are shown at A and B, respectively. These may be connected by'any Well-known form of link circuit such as L, arranged to apply ringing current from a source 1 through an interruptenQ and a marginal tripping relay 3 to the called sub-- scribers line. For the purpose of supplying ringing tone current an interrupter 4 and a battery are provided. It is to be understood, however, that any other suitable source of current, as might be obtained from a motor driven generator, could also be used. Current from this source is applied to the primary windings 25 of a transformer 5. The currentinduced in the secondary windings 26 t transformer is smoothed outby a filtering circuit composed otre tardation coils 27 and condensers 28. The filtered current is modulated periodically by the interrupting device 8 thereby simulating the modulating of the audible harmonic components of a 16-cycle ringing current wave as explained above. This interruptingdeviceis arranged so that the load on the source of interrupted current is main tained approximately constant, irrespective of the energized or deenergized condition of relay 9, which relay applies the signaling tone current to the tip conductor of the link circuit, to signal station A that station B is being signaled. In the circuit leading to the contact of relay 9 is a filtering device, consisting of a condenser 10 and retardation coil 11, the function of which is to smooth out the waves after each interruption of the interrupter 8. Through the back contact of relay 9 is connected a resistance 12, the electrical equivalent of the resistance 13, whereby current passing through the last mentioned filtering device is maintained approximately constant with relay 9 normal or energized.

As shown in Fig. 2 the current produced by the source 1 possesses numerous harmonics which affect the wave form of such current. As previously mentioned, in one system widely in use, the higher audible harmonics superimposed upon the 16-cycle current are transmitted to the calling subscriber through a repeating coil similar to repeating coil 21. In such a case the current wave flowing over the calling line assumes, in general, the form shown in Fig. 3. Although there may be many more harmonics present in this current, only a sulficient number have been shown to illustrate the form produced. 7 This current has been found to produce a distinctive and pleasing tone in the calling subscribers receiver. The current produced by the battery, the commutator 41, the repeating coil 5 and associated apparatus and modulated by the interrupter 8 assumes the wave form shown in Fig. 1. It will be noted that the current is of a frequency corresponding to one of the audible harmonics shown in Fig. 3 and is subjected to a modulation by interrupting device 8 to produce a wave form similar to that of Fig. 3. However, it is not affected by variations in the source of ringing current.

It is thought that the invention may be more fully comprehended from the following detailed descri1i)tion. It is assumed thatthe subscriber of line A desires a conversational connection with the subscriber of line B and that connection with the callin line has been established in the usual manner. The connection is then comipleted .in the well-known manner over the link circuit L by an operator inserting a plug 1 1- into jack 15. Relay 16 is operated over a circuit extending from grounded battery, through the winding of relay 16, contacts of relays 3 and 17 (which contacts short circuit the winding of relay 17), sleeve contacts of plug 14 and jack 15, and resistance 18 to ground. Ringing current is then supplied to the line of subscriber 13 from the source 1 over the following path: source 1 of ringing current.

collector ring 19, segment 6 and brush 7 of interrupter 2, winding of tripping relay 3, lower alternate contact of relay 16, ring contacts of plug 14; and jack through the apparatus of station B, tip contacts of ack 15 and plug 14, upper alternate contact of re lay 1G to ground through the resistance 13. Another path to ground for the ringing current may be traced through the upper righthand windin 20 of repeating coil 21. A. very small proportion of the ringing current, however, reaches ground through this path because of the shunting effect of the resistance 13. This path is of very low impedance so that the potential drop of the signaling tone current from the interrupter t will be substantially independent of variations in the number of connected lines.

When the brush 7 of interrupter 2 comes into contact with segment 6, relay 9 is energized through condenser 22. This causes interrupted battery current from the high speed interrupter 4 to be furnished to the link circuit through the alternate contact of relay 9 over a circuit path which will now be described.

Relay 23 is normally energized through an obvious circuit including condenser 21-. Its function is to disconnect the supply of interrupted current from interrupter 1 when ringing current from source 1 fails. Assuming that relay 23 is operated a circuit may be traced from battery through the interrupter 4, contact of relay 23 and the windings 25 of transformer 5 in parallel to ground. Current is induced in the secondary windings 26 and the flow of currentis as follows: from the ground connection between the center of windings 2G in parallel. through the filter circuits includin inductances 27 and condensers 28 to unction point 29. lVith the interrupter S in the position shown on. the drawing there are two paths to ground from point 29 as follows: point 29, resistances 30 and 31 to ground; the other path includes resistance denser 10, impedance coil 11, contact of relay 9 and resistance coil 13 or 12 to ground, depending upon the operated or non-operated condition of relay 9. Because of the equal resistance of 12 and 13 the electrical conditimi oi: the circuit of interrupter S will, accordingly, remain apl'u'oxiinutely constant with relay 9 operated or non-operated. ll has been found that the very short period during which the contact of relay 9 is opened, results in an interruption of the tone that can only with difliculty be detected. When the armature 33 of interrupter 8 is in the right-hand position then resistance 32 is shunted by resistance 34 causing an increase in current through the path of the alternate contact of relay 9. When the armature 33 is in the left-hand position resistance 34: then 32, con- Jill! liil) shunts resistance 30, and the current through resistance 31 is the greater. Resistance 31 sisting of the impedance coils 27 and condensers 28, is to smooth out the sharp peaks in the current wave which may be due to the interrupter 4. After interruption by the interrupter 8 any sharp irre 'ularities which are ire-introduced by the interrupter 8 are filtered out by the filter composed of the impedance coil 11 and the condenser 10.

The potential drop across resistance 13 is" utilized as in the aforementioned copending application of Philip Husta, to supply signal current tone to station A, by way of the upper alternate contact of relay 16, the tip conductors of link circuit L and the winding 20 0t repeating coil 21 to ground. The subscriber at station A will accordingly know that called station B is being signaled and the tone which is heard will by reason of the periodic modulation by the interrupter S be similar to that now obtained in existing installations from the audible harmonic components of sixteen cycle ringing current.

Inasmuch as the link circuit L shown on the drawing is well known in the art and is not part of this invention, only so much thereof as is necessary to an understanding of the invention has been disclosed and described herein. The circuit arrangements employed at stations A and B have been omitted since they may be of any usual type.

What is claimed is:

1. In a telephone exchange system, a calling subscribei"s station, a called subscribers station, a link circuit for interconnecting the stations, a source oi signaling current to call the called subscribefis station, a second source of signaling current to signal the calling subscribers station that the called subscribefs station is being called, means for modulating the current trout said second source, means tor applying to said link circuit current from said second source while current from said first mentioned source is being simultaneously applied, and means for maintaining approximately constant the electrical characteristics of said second source of current during its application to the link circuit.

2. In a telephone exchange system, a calling subscribers station, a called subscribers station, a link circuit for interconnecting the seationaa source of signaling current to callthe called-subscribers station, a second source of signaling current to signal the calling 'subscribens station that the called SU'bSGTliQGlk-S station is being called, means" 'tor modulating current from said second source, means -lor applying to said link cir-v cuitcurrent :trom saic. second source while current from said first mentioned source 18 "being siinirltaneously applied, the electrical continuity of the link circuit being maintained, and means for maintaining approXi mately uniform the electrical constants of the circuit of said second source of current during its interrupted application to the link circuit.

3. In a telephone exchange system, a calling subscribers station, a called subscribers station, a link circuit for interconnecting the stations, a source oi": signaling current to call the called snbscribers station, a second source of signaling current to signal the calling subscribers station that the called subscribers station is being called, means for applying to the said link circuit periodically interrupted current from said first mentioned source and periodically modu lated current from said second source of current simultaneouly, the inductive continuity of the link circuit being maintained, and means for maintaining the electrical constants of the circuit of said second source of current approximately constant during its periodic modulation to maintain constantthe character of the signaling tone obtainable from said second source of current.

i. A telephone system comprising a calling and a called station, separate sources of signaling current forsaid stations, means for periodically applying current from one of said sources to one of said stations, means for interrupting current from the other of said sources, means for modulating said interrupted current, and means for applying said modulated current to the other of said stations contemporaneously with the application of current from said first mentioned source to said first mentioned station.

5. A telephone systen'i comprising a calling and a'called station, sources of. signaling current for said stations, means for periodi cally applying current from one 01E said sources to the called station, means for interrupting the current from the other OIli said sources, means for modulating said interrupted current, and means for applying said modulated current to the calling station contemporaneously with the application of cur rent from said first mentioned source to said called station.

6. In a telephone system, telephone stations, separate sources of signaling current for said stations, means for periodically applying current ttrom one'of said sources to one of said stations, means for interrupting current from the other of said sources, means for modulating said interrupted current, and means responsive to the application or said first mentioned source to 5 said first mentioned station for applying said modulated current to the other of said stations.

7. The method of informing a calling subscriber that ringing current is being sup- 10 plied to a called station which comprises generating a plurality of currents one of Which is an audio-frequency and the other is a lower frequency, modulating one of said currents, and supplying the modulated and unmodulated currents to the calling subscriber.

In Witness whereof I hereunto subscribe my name this 10th day of September, A. D.

LELAND J. STACY. 

